Compositions that are polymerized and/or crosslinked by exposure to actinic radiation (e.g., ultraviolet light) are used in a number of applications, such as coatings, adhesives, and the formation of molded articles (e.g., 3-dimensional shaped articles, such as gaskets and lenses). Such compositions typically include reactants having one or more ethylenically unsaturated groups that are radically polymerizable. Reactants having one or more ethylenically unsaturated groups that are radically polymerizable are not typically themselves rendered polymerizable by exposure to actinic radiation. The presence of an initiator that is activated by exposure to actinic radiation (typically referred to as a photoinitiator) is often required. Upon exposure to actinic radiation, the photoinitiator generates one or more initiator radicals that serve to initiate radical polymerization of the radically polymerizable reactants of the composition.
To achieve a sufficient level of initiation, an excess of photoinitiator is typically included in the curable composition. In many applications, photoinitiation is undertaken in the presence of oxygen, which inhibits radical polymerization, thus, requiring a further increase in the level of photoinitiator initially present within the curable composition. As such, the resulting cured material typically includes residual photoinitiator.
In addition to generating initiator radicals upon exposure to actinic radiation, photoinitiators typically also form or generate non-initiating co-products that that do not initiate radical polymerization. The photoinitiator itself, and the non-initiating co-products thereof typically have relatively low molecular weights, and as such, often volatilize and/or migrate from the resulting cured product. Such volatility and migration (or mobility) is generally undesirable due to, for example, related unpleasant odors and/or contamination of a surrounding matrix material (due to migration there-into). With photopolymerizable compositions used in food or medical applications, such as packaging adhesives, volatilization and mobility of residual photoinitiator and/or non-initiating co-products into the packaging matrix is typically undesirable as it may result in contamination of materials in contact with or contained within the packaging (e.g., food items or pharmaceuticals).
Polymeric photoinitiators, having higher molecular weights, have been developed in an attempt to minimize the volatility and/or migration associated with lower molecular weight photoinitiators. Polymeric photoinitiators are typically non-uniform with regard to, for example, polymer backbone structure, the terminal ends of the polymer, and/or polymer molecular weight, which may lead to variable properties and reactivities of the polymeric photoinitiator.
It would be desirable to develop new photoinitiators having reduced or minimal volatility and/or migration associated therewith. In addition, it would be desirable that such newly developed photoinitiators also have consistent properties and reactivities.